1. Field of the Invention
The present invention relates to a method for producing a titanium dioxide (TiO2) photocatalyst and a titanium dioxide photocatalyst produced by the method. More specifically, the present invention relates to a method for producing a titanium dioxide photocatalyst using a sol-gel process wherein an acid and a base are added in two separate steps to achieve high mesoporosity and improved surface characteristics while maintaining an anatase crystal structure even at high temperatures, and a titanium dioxide photocatalyst produced by the method. The present invention also relates to a titanium dioxide photocatalyst doped with sulfur and zirconium that possesses catalytic activity even in the visible region, and exhibits excellent surface characteristics in terms of surface area, pore size, pore volume, etc. and improved catalytic activity.
2. Description of the Related Art
Since Honda and Fujishima of Tokyo University reported the photocatalytic degradation of water using a titanium dioxide photocatalyst in the journal Nature in 1972, much research on novel photocatalysts using semiconductor materials (e.g., titanium dioxide) has been consistently conducted for scientific and commercial purposes. Particularly, titanium dioxide photocatalysts based on nanotechnology, which is currently in the spotlight, have been used throughout the world as means to remove pollutants causing serious environmental problems. Titanium dioxide photocatalysts have been found to offer the possibility of energy storage in recent years. It is thus anticipated that titanium dioxide photocatalysts will be continuously researched as promising energy storage materials. A disadvantage associated with the use of titanium dioxide as a photocatalyst is that light of short wavelengths in the ultraviolet (UV) region is required. For these reasons, there is a continuing need to modify pure titanium dioxide to develop photocatalytic materials capable of possessing photocatalytic activity even under visible light. Doping with metallic or non-metallic materials, surface modification, composite formation with other semiconductor materials and so forth have heretofore been known as modification methods of titanium dioxide.
Titanium dioxide photocatalysts doped with metallic materials have been extensively investigated for a long time. Most of the titanium dioxide photocatalysts doped are expected to react under visible light because a reduction in band gap due to the metallic materials is observed. However, the reactivity of the titanium dioxide photocatalysts is known to be poor due to the possibility that the time when electrons and holes separately exist may be relatively short depending on the kind and amount of metals used in comparison with pure titanium dioxide. In attempts to overcome the problems of the doping with metallic materials, titanium dioxide photocatalysts doped with non-metallic materials have been developed. According to a recent report in the journal Science, doping titanium dioxide with a non-metallic material, such as nitrogen or carbon, induces a decrease in band gap, resulting in high reactivity under visible light. Since then, numerous studies around the world have focused on titanium dioxide photocatalysts doped with non-metallic materials.
In recent years, efforts have been made to develop titanium dioxide photocatalysts with better catalytic activity that are doped with both metallic and non-metallic materials rather than with a non-metallic material only. Such efforts are still in very early stages and research is actively underway to find suitable combinations between metallic and non-metallic materials.